Diversity gains and receiving complexity are considered important performance measures when a multiple antenna communication system is designed. Various multiple antenna transmission methods for obtaining a maximum diversity gain have been suggested, and one of them is an Alamouti transmission method.
According to the Alamouti transmission method, a signal transmitting apparatus includes two transmitting antennas and a data rate is 1. Since the Alamouti transmission method has low complexity while having a maximum diversity gain, it is widely used. However, when the signal transmitting apparatus uses more than three transmitting antennas, the data rate may not be 1 to obtain the maximum diversity gain and the low receiving complexity. In addition, there is a problem in that the receiving complexity may be considerably increased in order to obtain the maximum diversity gain and the data rate of 1.
To solve the above problem, a method in which two respective Alamouti transmission blocks as given in Equation 1 are used when the number of transmitting antennas is 4 has been suggested (“IEEE802.16e/D12, Part 16: Air interface for fixed and mobile broadband wireless access systems”, October 2005, p. 473-474).
                    (                                                            s                1                                                                    -                                  s                  2                  *                                                                    0                                      0                                                                          s                2                                                                    s                1                *                                                    0                                      0                                                          0                                      0                                                      s                3                                                                    -                                  s                  4                  *                                                                                        0                                      0                                                      S                4                                                                    s                3                *                                                    )                            (                  Equation          ⁢                                          ⁢          1                )            
In Equation 1, respective rows in a matrix are signals transmitted to respective transmitting antennas, first and third columns are signals transmitted at a time k, and second and fourth columns are signals transmitted at a time K+1. The Alamouti transmission block including the first and second columns and the Alamouti transmission block including the third and fourth columns are transmitted by using different orthogonal resources (different subcarriers in a case of orthogonal frequency division multiplexing).
However, the transmission method as in Equation 1 submits to loss of the diversity gain to achieve the low receiving complexity and the data rate of 1. In addition, it is not appropriately used for a transmitting apparatus having 3 or 5 transmitting antennas.